Leftward message from the biotin cluster of Escherichia coli will be measured in strains bearing deletions of all known rightward genes, to see whether genes of the right transcript have any regulatory effect on leftward transcription. The nature of insertion that inactivate both leftward and rightward transcrption will be investigated by heteroduplexing with phages bearing known insertions. Deletions fusing genes of the left operon of lambda prophage to the bacterial trp promoter will be isolated from strain KS 507, which carries lambda inserted into trp. We will continue to examine mutations having regulatory effects on genes of biotin biosynthesis for their effects on biotin holoenzyme synthetase. BIBLIOGRAPHIC REFERENCES: Ketner, Gary and Campbell, Allan. Operator and promoter mutations affecting divergent transcription in the bio gene cluster of Escherichia coli. J. Mol. Biol. 96, 13-27 (1975). Campbell, Allan. Significance of constitutive integrase synthesis. Proc. Nat. Acad. Sci. U.S. 73, 3 (1976) (in press).